The invention relates to pipe joining More particularly, the invention relates to pipe joining by electrofusion.
A well developed field exists in polymeric piping systems. Perhaps the most well known thermoplastic material for pipes and pipe fittings is polyvinyl chloride (PVC). PVC pipes and fittings are typically joined to each other via the use of a solvent cement to form joints characterized by solvent weld/bonds. Other solvent-weldable materials include chlorinated polyvinyl chloride (CPVC) and acrylonitrile butadiene styrene (ABS).
It may be less practical to solvent weld other thermoplastics such as polyethylene (PE, including high density polyethylene (HDPE) and low density polyethylene (LDPE)), polypropylene (PP), polystyrene (PS), and polybutylene (PB). Thermal welding provided via electrofusion is an alternative to solvent welding. United Kingdom Patent Application GB2260381A and US Patent Application Publication US2006/0016552A1 disclose systems wherein resistive heating elements are at least partially embedded in fittings. A pipe may be inserted into the fitting so as to be encircled by the heating element.
U.S. Pat. No. 3,506,519 discloses a collar/fitting assembly comprising a plastic fitting, an electrofusion collar (i.e., containing the heating element), and a clamp. Additionally, such collars are available from Georg Fischer Harvel LLC, Little Rock, Ark. and Easton, Pa., US (e.g., under the trademark Fuseal II). Several of the Fuseal II collars include an inner wall containing the heating element and a radially spaced-apart segmented outer wall for engaging the clamp. The electrofusion collar is inserted into the fitting socket and, in turn receives the end of a pipe (or a male fitting spigot). The clamp is tightened around the fitting (or collar outer wall) to radially compress the fitting and collar to the pipe to insure no air enters the welding zone.
The heating element may be energized by an electric power source to heat the fitting and the pipe sufficiently to weld the two together. Exemplary power sources are found in U.S. Pat. No. 5,911,895 and are available from Georg Fischer Harvel LLC, Little Rock, Ark. and Easton, Pa., US (e.g., as the MSA family of electrofusion units).